Recently, with the emergence of the Internet of things, interest has grown in direct communication between user equipments or in D2D (device-to-device) communication technology, which is a kind of communication method for interworking with smart devices. The D2D communication is a communication scheme in which adjacent devices directly communicate with each other without the relay of an infrastructure of the existing wireless communication systems, such as base stations or APs (Access Points).
In the D2D communication environment, each node including a mobile user equipment discovers other user equipments near the same either independently or through the support of the base station, and establishes a communication session with the discovered user equipment in order to thereby transmit and receive traffic. Since the D2D communication can solve the traffic overload problem by distributing the traffic that is concentrated on the base station, and can provide new communication services based on the proximity between user equipments, it has been highlighted as an element technique for next generation mobile communication technology following 4G.